A light emitting diode comprises a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively.
In LED applications, an LED semiconductor chip includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which causes the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light. The ability of LED semiconductors to emit light has allowed these semiconductors to be used in a variety of lighting devices. For example, LED semiconductors may be used in general lighting devices for interior or exterior applications.
Various techniques have been tried to improve the light output and directionality LED arrays. For example, with regards to directionality, the addition of a lens that covers the entire LED array has been used in an attempt to extract light and control the directionality of the emitted light. For example, a conventional array of LEDs will normally create a round beam pattern on the ground. Unfortunately, this technique to control the directionality of light emitted from an LED array does not perform as well as desired. For example, it is desirable to have a way to create specific beam patterns and to focus those beam patterns in a specific direction.
Accordingly, what is needed is a simple and cost efficient way to focus and direct the light emitted from an LED array.